Gas analysis



May 15,1945. 1 HoRvlTz i 2,376,145

GAS ANALYSIS Filed March 2a, 194;

. most loi this pure oxygen is obtained electro-` lytically, and isfrequently contaminated withV Patented May 15, 19:45

UNITED STATES PATENT OFFICE l 'GASIS ,c

l Leo Horvitz, Houston, 385 592 I Claim.

' in minute traces in these gases.

As has already been indicated.' in that method m of geochemicalprospecting/in which soil gases are analyzed fortheir content ofhydrocarbons and/or hydrogen, these constituents are found in extremelyminute amounts, ranging from a few parts per million .to several hundredparts per million by volume. In one particular method soil samples arecollected and a gas sample is collected from the soil by desorption,this gas being then analyzed for its content of hydrocarbon and/orhydrogen. constituents, be it hydrocarbon`or hydrogen, is

-expressed in parts per billion by weight of the soil sample and mayvary from. a few parts per billion to several hundred parts per billion.As f will be understood, the analytical method employed for this purposemust be extremely sensitive. It should be capable of measuring hydrorcarbons present in a gas at least as accurately as to a few parts permillion by volume.

It has been found that in analyses of this type '3 errors may creep intothe results by reason of impurities in the air or oxygen used for thecombustion of the combustible constituents which are being analyzed for.Where hydrocarbons are beingsought and air isemployed to support thecombustion, it may be that the air will contain combustible matter, suchas hydrocarbons; car- 'bon monoxide or hydrogen, which will influence Athe results of the analysis, which, as will be unv derstood, aremeasured in terms of carbon dlox- 40 ide 'and water produced by thecombustion of the significant constituent.. Even` when pure oxygen isemployed, difficulty is encountered when the analysis is conducted byreason oibthel fact that minute' amounts of hydrogen.

To illustrate the difliculty more specifically, a prospect was run bythe method in which soil gas is analyzed for hydrogen, and highvaluesof\ hydrogen were found. The combustion-supportn/this case thesignificant 2n hydrogen which. upon inquiry as to the method employedfor the manufacture of the oxygen,

was found to be hydrogen resulting from the electrolysis of water.Again, in many cases in which air is employed for the analysisof gaseoushydrocarbons, it has been found that room-air in a laboratory containshydrocarbon gases which leak into the atmosphere fromthegas jets in suchplaces.

According to the present invention,v therefore, thecombustion-supporting gas used for the analyses of gases containingminute amounts of combustible material is first subjected to a treatmentcapable of removing from it any combustible material that may becontained therein. In vmany instances suilicient purification can berealized by subjecting the combustion-supporting gasto very lowtemperatures. such as( the temperature of liquid nitrogen or liquid air,or liquid hydrogen. Liquid hydrogen is expensive and liquidv nitrogenand liquid air do not produce a low enough temi perature to insure thecomplete removal of sub' stances suh as methane, carbon monoxide andhydrogen, and for this reason it is desirable, and in fact preferable,to combine, with the refrigerating step, a combustion step. Thatis tosay, the air or oxygen to be 'used for combustion, is itself firstsubjected to combustion and to refrigeration, atleast after thecombustion.

jIn a practical operation according to the present invention the air oroxygen to be used for the combustion of the gas to be analyzed is rvst4passed through a trap refrigerated .by liquid nitrogen in which anycondensible constituents will be removed, The residual air or oxygen isthen conducted to a combustion chamberwhere it is subjected tocombustion, and is then` again subjected to refrigeration to remove anyprod' ucts of combustion, namely, carbon dioxide .and water. The gas isthen suiliciently pureto .beiA admitted to the combustion ,zone in whichthe gas to be analyzed is burner/i. It'will be uderstood, of curseythatboth in the' initial .and

in the final refrigeration steps any carbon dioxide porting gas isremoved. It is sometimes desirable to pass the gas through a dehydratingvagent beforeintroducing it into the purication system so that thepossibility of any water collecting o n the wallsof the conduit andbeing later'picked up by the purified gas before its use in theanalytical step is avoided. 'Ihis initial dehydration step is notnecessary in most types of apparatus lemployed for this Apurpose becauseall of the portions of the apparatus with which tue" puri,-

fied combustion supporting gas comes into contact, are maintained at anyextremely low pres- `'sure or conversely, high vacuum, and areintermittently flamed so that collection of water o the walls isprevented.

The present invention will be more clearly understood from the followingdetailed description of the accompanying drawing in which Fig. 1 is afront elevation in diagrammatic form of one type of apparatus suitablefor the performance of the method of the present invention; and

Fig. 2 is a modified form of apparatus useful for this purpose.

The arrangement shown in Fig. 1 is identical in essential features withthat shown in Fig. 2 of the drawing of my copending application Ser. No.183,960, led January 8, 1938, now U. S. Patent No. 2,287,101, of whichthe present application is a continuation in part. A

Referring particularly to Fig. 1, numeral I designates the point ofentry of the gas to be analyzed. The system is provided withL aplurality of mercury oat valves designated by numerals 21 3, 4, 5, 6,'I, 8, 9, I0 and il. Line I is connected Athrough valves 2 and 3 to atrap I2 which is preferably identical with that described in Patent No.2,177,139, issued October 24, 1939. This trap I2 is immersed in asuitable refrigerant contained in a receptacle I3. yThe outlet of theAtrap is connected through valve to a pump, not shown. Between valve 5and the outlet of the trap is a branch line I4 which is connectedthrough valve 4 to a McLeod gauge, or other suitable gauge, formeasuring pressure in the system.

A line I5, which includes valves B and 1, has one of its ends connectedbetween the outlet of trap I2 and the valve 5 and the other of its endsconnected to line I between valves 2 and 3. Arranged in this linebetween the valves 6 and 'I is la collection cell I6 and a pump II whichwill usually be a mercury diffusion pump. The direction of flow of thegas through the cycle formed by line I5 and the trap I2 is indicated fonthe pump by an' arrow. Between valve 'I and line I there is arranged inline I5 a combustion chamber I8.

lA line I9 has its two ends connected to the line I5, one end ahead ofthe collection cell I6 and the other end between the pump and valveA l.This line I9 includes valves 8 and 9, and also includes a 4trap 20similar to trap I2 and adapted to be partially immersed in arefrigerating medium in a receptacle 2 I, and a combustion chamber 22-.It may be noted that each of cornbustion chambers-I8 and 22- is providedwith a suitable filament 23 which maybe electricallyv heated to effectthe combustion.

A branch line 24 carrying valve I I is connected to line I9 ahead oftrap 20 and is provided with a stopcock 25 and a drying tube 26. Thefree end of line 24 is open to the atmosphere or to a source of oxygen.A second branch line 21 is connected to line I9 ahead of the. trap andinthe pressure in this part ofthe system is sumciently reduced, as willbe indicated by a manomsuch as calcium chloride.

eter suitably located, the valve I is closed and valve II and stopcockare opened. It may be mentioned here that the system is usuallyevacuated to a pressure of 10-5\mm. of mercury or less. When valve II-and stopcock 25 are opened, air or oxygen, as the case may be, is drawninto the system until the pressure in the system rises to 20 or 30 mm.At this point stcpcock 25 and valve II are closed. Itis to be notedthat, in entering, the air passes through the drying tube 26 whichcontains a suitable dehydrating agent, The tube may also contain an`alkaline hydroxide to remove any carbon dioxide 4present in the initialgas.

With valves I and Il closed, valves 8 and 9 are opened, and the gas inthis portion of the system is circulated -by pump Il, the filament incombustion chamber 22 having been heated. In its repeated vpassagethrough the combustion chamber .the gas is freed from any combustibleconstituents. Complete combustion of any such constituents in the gaswill ordinarily beeffected in a minute or two. During the combustionstep, if desired, orimmediately thereafter, the receptacle 2'I is filledwith a refrigerant, such as liquid nitrogen. The gas is continuouslycirculated through the trap 20 surrounded by this refrigerant with theresult that the products of combustion, namely, caribon dioxide andwater, are condensed and deposited in the trap 2c.

4Valves 8 and 9 are then closed, valve I0 is opened and the trapl andcombustion chamber are pumped out. This leaves cell I6 and that portionof line I5 which is between valves 6 and 'I lled with purifiedcombustion supporting gas.

Before the gas to be analyzed is introduced into the system valve 5 isopened and the trap is evacuated by the pump connected to the outer endof valve 5. In this case the pressure, is also reduced to 10-5- mm. ofmercury or less. The valve 5 is then closed,`valves 2 and 3 are openedand the gas to be analyzed` is introduced into this portion of thesystem. The trap is surrounded by a refrigerant, such as liquid nitrogenI which maintains a temperature at hich the constituent which is to beanalyzed or is condensed and collected. Ordinarily, this constituentwill be hydrocarbons heavier than methane. In the i event that theanalysis is to be conducted for then measured with a McLeod gauge.frigerant is again applied to trap I2 and the pressure again measured.From the difference hydrogen alone, it will, of course, be necessary toinclude further traps in the system to eect a suitable fractionation toisolate the hydrogencontaining fraction in trap I2 as explained in mycopending application Serial No. 183,960 now U. S. Patent No. 2,287,101.

With the constituent to be measured condensed and deposited in trap I2,valve 2 is closed, valve 5-is opened and the residual gas in thisportion of the system is pumped out. Valves 3 and 5 are then closed andvalve 4 opened. Refrigeraht is removed from trap I2 resulting invaporizationof the condensed constituents. Pressure is The rein readingsthe volume of gas intially present is calculated. Valve 4 is thenclosed, valves 3, 6 and 1 are opened and the refrigerant is removed fromtrap I2 allowing the collected constituent to vaporize or gasify. Thefilament 23 in combustion chamber I8 having Ibeen in the meantime heatedup, the pump IIis started and gas circulates, in the cycle passingrepeatedly through the combustion chamber. able p eriod is allowed forcomplete combustion,

After a suitusually not more than a few minutes, the refrigerant isagain applied -to the trap I2, while the circulation is continued, andthe products of combustion, namely, water and carbon dioxide, arecollected in this trap.- Valves 6 and 1 are 5 then closed, valve isopened, and residual gas is withdrawn from the system. Valve 5 is then'closed again, and valve 3 is closed and valve 4 -is,opened. Therefrigerant is again withdrawn from'ythe trap with the result that theVwater lo and carbon dioxide vaporize and give a pressure reading on theMcLeod gauge which is a measure of the quantity of these constituents.,If desired, after this measurement the trap can b again. immersed in arefrigerant maintained at about l5 80 C. to condense out the water, andthe resulting pressure in the system, as indicated by the McLeod gauge,will be that due to carbon dioxide alone.l The water can then bedetermined by difference.

In Fig. 2 is shown only the" purification system for the combustionsupporting gas. In this case this gas, be it air or oxygen, isintroduced into thesystem through line provided with a stopcock 3i and amercury. seal valve 32. The other 25 l mercury seal valves in thissystem are designated by numerals 33 and 34. Line 30 is connected to thegas analytical apparatus (not shown) through the valve 34. Branch line35 is connected to line 30 andto one side of a trap 36 adapted to be 30immersed in a refrigerating medium carried in a receptacle 31. The otherend of this trap is connected through a stopcock 38 to a collectionreceptacle 39 which also serves theipurpose of a combustion chamber, Tothis end, receptacle 33 35 is provided with a suitable filament 40 whichmay be vheated electrically.

Line 30 is provided with a secondbranch line 4l which is connectedthrough valve 33 to a pump (not shown), In the preparation of the 40combustion supporting gas for the analytical step by the use of thisapparatus, valves 32 and 34 `are closed, valve 33 is open. and thesystem, in-

cluding the trap and the collection receptacle, stopcock 38 being open,is evacuated as previously 45 described. After evacuation valve 33 isclosed and valve 32 andstopcock 3| are opened, per- Y mitting thel airor oxygen to enter thesystem.

At this time the trap 36 may be immersed in a suitable refrigerant,"such as liquid nitrogen, so as to cause the deposition of condensableimpuri-,f ties, such as carbon dioxide and water and heavy hydrocarbons,if any, in the trap 36, the re sidualgas being permitted to go into'there-v ceptacle 33. When a suitable pressure is obtained in the system,which may be any desired pressure and is usually up to about a half anatmosphere, stopcock 3| and valve 32 are closed. At this point it isusually desirable to close stopcock 38, open valve 33, remove therefrigerant from the trap 33 and again evacuate the portion y of thesystem so opened to the pump.

After or during this pumping-out step, the la ment 40 can be heated andany combustible material contained in a receptacle 33 burned. Valve 33is again closed, stopcock 33 is opened, and valve 34 is opened to permitthe introduction of the gas into the analytical system. -It is importantthat, when stopcock 33 is opened this time, the trap 36 be immersed in arefrigerant, such as liquid nitrogen, so that'in the passage of the gasfrom receptacle 33 to the analytical apparatus any products ofcombustion, namely carbon dioxide and water, contained therein, will bedeposited in the trap leaving only puriiied gas for introduction intothe analytical system.

The air purification system shown in Fig. 2 cor'- responds to .thatshown in my copending application Ser. No. 382,607, filed March 10,1941, and entitled Gas analysis. To this extent the present applicationis a continuation-impart of Ser. No. 382,607.

It will be apparent that changes vin the specic procedure described canbe made without depart' ing from the v'scope of th'e present invention.The particular temperatures and refrigerants mentioned aswell as theparticular times of operation will change with diiei'ent gases and withdiierent types of apparatus. l

The nature and objectsv of the present invention having been.thus'described and illustrated, what is claimed as new and useful is:

In an apparatus for analyzing gases for their content of combustibleconstituentsI present therein in minute amounts, in combination, meansfor separating and isolating'from said gas said combustibleconstituents, means forming with said first mentioned means a closedcirculating sys'- tem including a gas collection receptacle and a pump,a second circulating system including said gas collection receptacle andsaid pump, a combustion chamber in said second circulating system, arefrigerating zone in said second circulating system, and meansforintroducing a combustion-supporting gas into said second circulatingsystem.

' LEO HORVITZ.

